1. Field of the Invention.
The present invention relates to electrical coupling connectors for connecting and disconnecting devices to and from other circuits and, more particularly, to connectors wherein the force required to insert such devices can be controlled.
The density of electronic circuits which can be provided in a single housing arrangement is increasing markedly. Monolithic integrated circuit chips, in particular, are experiencing increases in the density of circuits contained therein. As a result, the housings for such electronic components must provide an ever increasing number of terminals for making electrical connections to the electronic devices contained therein or thereon. That is, the increases in circuit densities in a housing leads to the need for greater numbers of input terminals, output terminals, power supply terminals and the like. Since the housings themselves are designed to also be as small as possible for achieving high circuit densities, these terminals for the housing are becoming smaller in cross section, and so more delicate, and are also being positioned closer to one another.
Such electronic devices must, at the very least, be tested before use. Often, there is also a desire to evaluate the performance of the system they are to be used in and, in doing so, there will be a desire to substitute various of such electronic devices into the circuits to thereby check system performance. These, and other kinds of uses, lead to a need for connectors which will electrically couple such electronic devices at the terminals thereof to other devices having electronic circuits in them, such as test circuit arrangements, system prototype circuits and the like. However, the increasingly delicate housing terminals provided on these electronic devices cannot withstand high stresses in inserting them into the connector, or even repeated moderate stresses resulting from such insertions. Nevertheless, a certain amount of stress is required because the contacts in the coupling connector must be solidly against the housing terminals if satisfactory electrical interconnections are to be made.
As a result, the use of so-called low insertion force and zero insertion force connectors has come about. Low insertion force usually means there will be contact means in the connectors which lead to some frictional force in inserting the device terminals therein. As the numbers of device or housing terminals increase, these individual pin-connector forces, though small individually, accumulate to the point that the total force required to insert the device becomes quite high, often unacceptably high.
Because of such results, zero insertion force connectors are commonly used, with the contacts in the connector either being (i) normally closed but openable, or (ii) normally open but closable. In the first instance, the contacts usually are of two sides made of an elastic, conductive material so that they are resiliently held against one another. This resilient force, then, is the only force which is applied against the device terminals, a force which may be inadequate to assure good electrical contact.
The alternative of normally open contacts also usually has a two sided contact of an elastic, conductive material which uses the resilient force available in the material to keep the two sides apart. Thus, the actuation mechanism for the connector must not only provide sufficient force to hold the device terminals but also sufficient force to overcome the resilient force of all of the contacts. Providing a force certain to overcome the resilient force of all the contacts can easily lead to too much force being applied against the device terminals. All this force is applied not only against the contacts but also against the plastic connector bodies which have a tendency to creep in these circumstances, especially if used at higher temperatures such as in device testing at such temperatures or in extended operation at such temperatures for purposes of finding early device failures (burn-in). Furthermore, force tends to limit the life of the connector because in these circumstances operation of the cam leads to wearing out the connector parts. Thus, a connector capable of avoiding these difficulties is desired.